This application is based on Korean Patent Application No. 2001-73733 filed on Nov. 26, 2001, the disclosure of which is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates in general to a micro-mechanical device, and more particularly to a micro-mechanical device having an anti-stiction layer and a method of manufacturing the device.
2. Description of the Related Art
Recently, many different types of micro-mechanical devices such as micro-motors, micro-gears, and micro-mirror devices have been developed. In micro-mirror devices, according to resolution, for example, 500,000 through 1,200,000 actuating micro aluminum mirrors having a size of 13-16 microns are disposed at intervals of 1 micron. Each of the mirrors, which is supported by a hinge, turns to the left or right at an angular width of ±10° in response to a signal generated from a digital board to form an image.
FIG. 1 shows a micro-mirror device as a micro-mechanical device disclosed in U.S. Pat. No. 5,331,454, entitled “Low Reset Voltage Process for DMD” and issued to Texas Instruments Incorporated (Dallas, Tex.).
In FIG. 1, when a driving voltage is applied between an address electrode 10 and a mirror 12, an electrostatic attractive force builds between the address electrode 10 and the mirror 12. The attraction between the two causes the mirror 12 to become inclined on a hinge 14, which is supported by a support layer 16. The hinge 14 twists and the edge of the inclined mirror 12 contacts or lands on a landing electrode 18 of a substrate 20. The mirror 12 may undesirably adhere to the surface of the landing electrode 18. The adhesion between the landing electrode 18 and the mirror 12 results in attractive inter-molecular forces between the two surfaces commonly referred to as Van der Waals forces. Van der Waals forces increase as the surface energy of a material increases, as the contact area between the surfaces increases, or as the contact time between the surfaces increases.
One technique to overcome the adhesion or stiction problem involves applying a voltage pulse train to the landing electrode 18. However, the amount of the applied voltage must be increased to depress an undesirable increase in the Van der Waals forces of the contacting surfaces. Finally, too much electrostatic attractive force builds between the mirror 12 and the landing electrode 18, such that the device may be damaged and possibly even causing the mirror 12 to snap off of its hinge 14.
In U.S. Pat. No. 5,331,454, powdered perfluordecanoic acid (PFDA) is deposited as a passivation material 34 on the landing electrode, as shown in FIG. 2. A method of vapor-depositing PFDA on the landing electrode 18 is disclosed in U.S. Pat. No. 5,602,671 in detail. Referring to FIG. 3, an oven 40 is preheated to 80° C. A source material 44, in this case PFDA, and a chip 46 are placed in a glass container 48. These are placed in the oven 40, which is evacuated by a valve 50 and backfilled through a valve 42 with dry N2. When the PFDA reaches its melting temperature, it produces a vapor that is deposited onto the surface of the chip 46. The lid of the container 48 is removed after about 5 minutes of deposition, and the oven 40 is evacuated. Only a monolayer of PFDA is left on the chip 46. The PFDA monolayer produces beneficial effects, including a low surface energy, a low coefficient of friction, and a high wear resistance.
Although the conventional techniques discussed above are generally thought to be acceptable, they are not without shortcomings. In particular, a method of evaporating a solid source material and performing vapor deposition, as disclosed in U.S. Pat. Nos. 5,331,454 and 5,602,671, consumes valuable processing time to heat the source material, causes pollution, and requires surface activation.
Moreover, since a monolayer of PFDA having no cross link has volatility, hermetic sealing is necessary to maintain a constant sealing atmosphere within a device. This necessity results in an increase in the manufacturing cost and complex processes. In addition, the reliability of a monolayer decreases at high temperature. Since a monolayer is deposited to a thickness of several tens of angstroms through about 100 angstroms, it is impossible to adjust the thickness of the monolayer suitable to the size of a device, to improve characteristics and reliability, and to increase a life span.